A power converter is a power processing circuit that converts an input voltage or current source waveform into a specified output voltage or current waveform. A switched-mode power converter is a frequently employed power converter that converts an input voltage waveform into a specified output voltage waveform. A power factor corrector is one example of a switched-mode power converter that is typically employed in off-line applications wherein power factor correction at the input and a stable, regulated voltage at the output are desired.
Power factor correctors generally employ a two stage topology, including a boost converter and a DC-DC converter. The boost converter generally includes a boost inductor and a power switch coupled thereto. The boost converter further includes a rectifying diode coupled to a node between the boost inductor and the power switch. The boost converter still further includes an output capacitor coupled across an output of the boost converter. The output capacitor is usually large to ensure a constant output voltage. The boost converter generally provides adequate power factor correction. Power factor is defined as a ratio of the actual power delivered to the load to a product of the voltage and current at the input of the boost converter.
An output voltage of the boost converter is always greater than the input voltage (e.g., a voltage of the AC source). The DC-DC converter, therefore, is employed to scale the output voltage of the boost converter down to a voltage required by a load. The DC-DC converter may employ any of the commonly known topologies, depending on such factors as the amount of power to be processed and the required efficiency.
The use of the boost converter in combination with the DC-DC converter generally results in lower efficiencies due, in part, to losses experienced in both the boost converter and in the DC-DC converter. A single stage power converter was developed to reduce the number of stages required to perform power factor correction and to provide a DC output voltage of a level employable by the load. Available single stage power converter topologies, however, require the use of a post regulator to maintain output voltage regulation. The post regulator stage, however, is also subject to losses and may reduce the overall efficiency of the single stage power converter employing the post regulator.
Accordingly, what is needed in the art is a switching circuit and method of processing power for a power converter that overcomes the deficiencies of the prior art.